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Strange Behavior for New Tubes in Preamp

 A while back I had a tube get noisy in my Van Alstine T-10 RB pre-amp. It uses two of the JJE88CC and I ordered a new pair of their stock silver pin JJE88CC directly from Audio by Van Alstine. The new tubes arrived quickly and sound great and the noise (high pitched squeal) is gone. 

In the meantime I have consulted the AVA website and this pre-amp can also use: 6922,  ECC88, 6DJ8, 6CG7, and 6N1P tubes. I confirmed these numbers with someone at AVA and they said that using these numbers will not void my warranty, as long as they are 6 volt tubes.   After some research and asking questions I ordered a balanced and matched pair of JJE88CC Gold Pins, a pair of 6922, and a pair of matched 6N1P Voshkod Rockets. 

I used an interdental brush dipped in CAIG D5 cleaner, then tapped to remove excess to clean the tube sockets, even though my preamp is just shy of a year old. I install the Gold Pin JJE88CC and wait as they warm up. This is when things get weird. As they are warming up the slight noise (that sounds like steady static) gets louder and louder. At first I have to put my ear to the speakers to hear it but after 20 seconds I can hear the noise in my listening position eight feet away. It increases in volume each second until I shut off the preamp. This is with the preamp volume turned completely down. I thought maybe there was D5 cleaner residue causing trouble in or near the sockets but I had carefully used a blower and thought I did a good job removing residual cleaner.  So I re-installed the stock JJE88CC tubes I received from AVA and everything sounds like normal. Normal has been a slight static noise with my ear close to the speakers.

Today, after a week of using the same stock JJE88CC tubes, I try again the new Gold Pin JJE88CC tubes and same thing.... with the preamp volume turned clear down the noise starts out barely audible but builds until it can be heard across the room... at which time I shut off the preamp.  I let the tubes cool and remove them. I install the new Voshkod Rocket 6N1P and they sound great with the normal hiss that I'm used to if I put my ear to the speakers.

I let the preamp cool and replace the two 6N1P with the two new 6922. Same increasing loud noise but sounds more like a slightly crackly static instead of a steady monotone static or hiss.

I'm fairly new to tubes so I hope you folks have some ideas why it effects just the gold pin JJ and the 6922. Thanks.

foamcutter
larsman's avatar
larsman
3,162 posts
 

@mashif - I tried the 'tapping treatment' too, and that did solve the first noise problem caused by something 'flaking off', and it was fine for awhile before making those really loud noises; I'm not going to risk my speakers. And I cooked these for quite a long time before using them.

I've been buying tubes a long time and I've never had any make noise just from being there, never mind loud horrendous noises - I do not consider that to be acceptable -  and these were Hytron Military 6SN7's. Maybe the gunshot noises were because they thought they were still in the military... 

sns
4,218 posts
 

@iseland Yes, some of those tubes may not be run within their design parameters. I can understand receiving bad tubes from time to time, but so many failures in such a short time? The other possible issue is amp no longer in spec, screeching original bad tube may have been result of misbehaving amp or perhaps that tube may have damaged amp to some extent.

billpete
396 posts
 

False alarm for me. I discovered that I had a bad CD. Speaker cables first, reversed them, problem solved. Next problem turned out to be a flaw in a new/used CD.  I have had bad tubes before but not this time. A relief really. 

pindac's avatar
pindac
3,964 posts
 

The average Tube User is not able to access an Oscilloscope or a Tube Tester. The average Tube user really does not know the quality of the Valve they are using, the Trust is in the supplier and what they are reporting with the sale advert.   

Put either device used to measure a Valves condition in front of myself and will not know how to use it, unless given special guidance.

I don't have to, I have support from others who knows exactly what is required from their own devices when measuring a Valve to see where it compares to the Manufacture Spec'.

It is very very easy for myself to learn what has been delivered usually within a few days of receiving the Valves if a short notice request is made to test and if pre planned and I have the time, delivered Valves can be tested within hours of being delivered.

I do know exactly the condition of the Valves I am to use in a circuit and as my Tranxs on some devices are Hand Wound - Bespoke and not repeatable, it is very important I make sure the circuit is at its optimum.

Many Valves have been returned for a full refund due to the Testing showing Valves to be quite different to what was the shown in the advertisement.

Chinese Import Valves will not be given the same support, the Companies do not accept returned data sent about their Valves, they only accept their measurements done prior to packaging and the sale occurring.

If Amp's cost multiple thousands to buy, and a certain Valve is able to cause damage to the Amp' if not in a particular condition to support the circuit. The likelihood is that the cost of a repair might exceed much more than swapping out a Valve that might have been at the Top End of pricing and thought to be perfect for that reason.

Do all that can be done in ones capacity to ensure their Valve Purchases are exactly as they believe they have purchased. 

My friend who is the Valve EE whom designed / built my PP Power Amp's has informed me to be very careful with Valve usage. I am knowing from guidance given that a bad Valve (unknown meaning to me) can take out the Amps Output Tranx's. These are Unique / Bespoke and not repeatable, new Tranx's would be required and a whole new End Sound would be the result, which from my end is totally not wanted. 

Hence, I am very very careful about what is introduced to the Circuit.         

     

wolf_garcia
6,898 posts
 

I've never had much luck with JJ tubes, and use NOS GEs in my preamp and amp (both use 6SN7GTBs) and they're dead quiet, sound great, and last a really long time. I won't tolerate hiss or any noise really as I know I don't have to.

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